SPI

The SPI port has a bunch of settings that the bus pirate can let you control.
The first one is the speed. SPI is not like I2C. It is synchronous and sends out its
own clock and this is what governs the speed. SPI is full duplex meaning that reading
and writing happens at the same time over two seperate data lines.

It is a master-slave protocal where all communication is initiated by the
master. Addressing is done through a dedicated slave select line to to each
peripheral.

SPI Lines are:

MISO - Master In Slave Out

MOSI - Master Out Slave In

SCL - Serial Clock Line

SS - Slave Select Line (for every peripheral)

A quick about SPI is that because it is a synchronous full duplex master/slave
bus, data can transfer can only be initiated by the master, including when the
master wants the slave to talk. This is why master has to send dummy bytes of
data when reading bytes back from the slave.